Pavers with a chassis and with a trailed, floating paving screed articulated on this chassis via tow arms, the angle of attack of the paving screed being adjustable with respect to the ground and the paving screed having a pre-strike-off and a baseplate coupled to a vibration drive, are known both without as well as with at least one tamper bar which can move up and down by means of a drive and which has a variable number of strokes (with regard to the latter, cf., for example, German Patent No. DE 198 36 269 C1).
The action of a tamper device in tamping/vibratory paving screeds consists in a metering action which results in a high degree of compaction and in uniform compaction with respect to the mix to be placed. In the metering paving process, excess mix escapes to the front via a slope in the front region of the tamper bar, depending on a defined resistance of the mix to deformation. Without a tamper device, the result is a much more non-uniform compaction in the layer laid by the paver. This leads, inter alia, to correspondingly large unevenesses following the subsequent rolling operation performed by a compaction roller.
Furthermore, it is known to at least partially compensate for the absence of metering action of a vibratory paving screed by means of height-adjustable pre-strike-offs which interact with a front edge of the baseplate of the vibratory paving screed, this front edge being folded upwards at 60° to 90°, in order to avoid a situation, particularly when placing thin layers, for instance asphalt wearing courses, where too much mix gets under the vibratory paving screed and a thicker layer than desired is thus placed. The absence of metering function is essentially attributable to the radius which results during folding of the front edge of the baseplate. Moreover, height-adjustable pre-strike-offs are very elaborate and expensive and also difficult to handle.
Owing to the absence of precompaction afforded by a tamper, the angle of attack of a vibratory paving screed is considerably greater, i.e. the rear edge, as seen in the paving direction, of the paving screed is situated considerably lower than its front edge. As a result, the baseplates of the paving screed wear very unevenly and thus prematurely. In addition, in the case of vibratory paving screeds which have, arranged behind a main screed, widening parts in the form of hydraulically extendable extension screeds or added-on screed parts, the large angle of attack of the screed means that the widening parts have to have their height adjusted very frequently in order to align the rear edges of the baseplates of the main screed and its widening parts with one another.